Datasheet

LTC3442
12
3442fb
For more information www.linear.com/LTC3442
OPERATION
APPLICATIONS INFORMATION
–
+
12
11
V
IN
ERROR AMP
1.22V
14µA
FB
R1
R2
C
P1
V
C
V
OUT
1
SHDN/SS
C
SS
0.7V
ENABLE SIGNAL
R
SS
SOFT-START
CLAMP
TO PWM
COMPARATORS
CHIP
ENABLE
3442 F05
–
+
V
CI
Figure 5. Soft-Start Circuitry
COMPONENT SELECTION
12
11
10
9
8
7
1
2
3
4
5
6
FB
V
C
R
LIM
V
IN
V
OUT
BURST
SHDN/SS
RT
SGND
SW1
PGND
SW2
V
IN
V
OUT
GND
R
T
MULTIPLE
VIAS
3442 F06
V
IN
Figure 6. Recommended Component Placement. Traces Carrying
High Current Should Be Short and Wide. Trace Area at FB and V
C
Pins Are Kept Low. Lead Length to Battery Should Be Kept Short.
V
OUT
and V
IN
Ceramic Capacitors Close to the IC Pins.
Inductor Selection
The high frequency operation of the LTC3442 allows the
use of small surface mount inductors. The inductor ripple
current is typically set
to 20% to 40% of the maximum
inductor current. For a given ripple the inductance terms
are given as follows:
L
BOOST
>
V
IN(MIN)
• (V
OUT
– V
IN(MIN)
)
f • ∆I
L
• V
OUT
H
L
BUCK
>
V
OUT
• (V
IN(MAX)
– V
OUT
)
f • ∆I
L
• V
IN(MAX)
H
where f = operating frequency, Hz
∆I
L
= maximum allowable inductor ripple current, A
V
IN(MIN)
= minimum input voltage, V
V
IN(MAX)
= maximum input voltage, V
V
OUT
= output voltage, V
I
OUT(MAX)
= maximum output load current